Reaction Rates & Factors - Study Guide

REF STUDY GUIDE: Big Ideas Use to answer form questions

1.Reaction rate measures how fast a reaction proceeds — how quickly a reactant disappears or a product appears — and it is distinct from the total amount of product, which is set by the limiting reactant. Two flasks running the same reaction can finish in 15 seconds or 3 hours and still produce the same total product; what changes is the speed of the rearrangement, not the chemistry. Rate is therefore a fifth piece of evidence for a reaction, alongside the W1 evidence types (color, gas, temperature, precipitate).

2.Collision theory explains the mechanism behind every rate factor: reactions happen only when particles collide with enough kinetic energy (≥ activation energy) and in the right orientation. Anything that increases the frequency of collisions (concentration, surface area) OR the fraction of collisions with enough energy (temperature, catalyst) speeds the reaction up. Temperature does both at once, which is why raising it ~10 °C often roughly doubles the rate.

3.A catalyst opens an alternative reaction pathway with a lower activation-energy hill, so a far greater fraction of collisions succeed; unlike a reactant, the catalyst is not consumed by the reaction and emerges intact (it can be reused). Enzymes inside your body are biological catalysts that make life-sustaining reactions fast enough at body temperature. Industrial catalysts let chemical plants run at lower temperatures and pressures than would otherwise be required.

DRAW KEY TERMS Google each → Images tab → sketch what you see

OTHER VOCAB: concentration · surface area

Reaction Rate

Speed at which a chemical reaction proceeds

Catalyst

Substance that speeds up a reaction without being consumed

Collision Theory

Reactions occur when particles collide with enough energy

Activation Energy

Minimum energy needed to start a chemical reaction

WRITE FOCUS QUESTION Your initial thinking

Bread dough rises in 45 minutes on a hot summer afternoon but takes over 3 hours in a cold winter kitchen. The yeast reaction is the same; only the speed changes. The same is true everywhere — rust forms slowly, fires burn quickly, milk spoils faster on the counter than in the fridge. Same atoms, same products: different conditions, very different rates.

Why does food cook faster on a hot day than a cold day?

I think...particles in warm food move FASTER, so they collide with oxygen and each other more often AND with more energy. More collisions = more reactions per second, which means a faster rate. On a cold day, the particles are sluggish, so the same reaction takes longer.

WRITE AFTER HOOK FORM Reflect before continuing

I learned that... reactions only happen when particles collide with enough energy (the activation energy) AND in the right orientation. Anything that increases collision frequency (concentration, surface area) or the fraction of collisions that have enough energy (temperature, catalysts) speeds up the reaction.

WRITE Temperature & Activation Energy

Station 1 — Temperature & Activation Energy

As temperature increased from 5 °C → 50 °C, rate ___ because: WENT UP — way up. A 10 °C rise roughly DOUBLES the rate, so 5 °C → 50 °C (~45° increase) sped the same reaction up roughly 16–30x. Same reactants, same products; only the SPEED changed.

Collision-theory explanation: hotter particles have MORE kinetic energy, so they (1) collide MORE OFTEN and (2) a bigger FRACTION of collisions clears the activation-energy hurdle. Both effects multiply, which is why temperature has such a huge effect on rate.

In my own words, "activation energy" is: the MINIMUM energy a collision must have to actually cause a reaction. Below Ea, particles just bounce off — no products form. Raising temperature shifts MORE particles above the Ea threshold.

CHECK DAY 1 CHECK-IN Before you leave

Q1: Based on today's investigation of reaction rates & factors, explain one key finding using evidence from your data. Connect your answer to this week's focus question: Why does food cook faster on a hot day than a cold day?

Food cooks faster on a hot day because the food's particles already have more kinetic energy, so when extra heat is added they hit the activation-energy threshold sooner. On a cold day the particles start out sluggish, so MORE energy has to be added before enough collisions are forceful enough to cause cooking reactions. Same chemistry, same products — temperature just changes how fast the rearrangement happens. A roughly 10 °C rise about doubles the rate.

Confidence:

Still building Getting clearer Ready to explain

Main idea I observed: powdered (high-surface-area) reactants react MUCH faster than the same mass in a chunk. Same amount of material, but the powder exposes far more particles per second to collisions on the outside surface.

Evidence from my data: the powdered sample bubbled / dissolved / changed color visibly faster than the chunk in the same time interval. Same total mass, same reactants — only the surface area changed.

I can apply this by: this is why we chew food (more surface area for digestive enzymes), why kindling lights faster than logs, and why factories grind catalysts into fine powders. To slow a reaction, do the opposite — keep things in big chunks or cool them down.

WRITE Catalysts & Reaction-Rate Design

The main idea about catalysts is...a catalyst opens an alternative reaction pathway with a LOWER activation-energy hill, so a much bigger fraction of normal collisions has enough energy. Catalysts are NOT consumed — they come out at the end intact, ready to be reused.

This connects to Week 1 (evidence of reaction) because...Week 1 evidence of a reaction was gas bubbles, temperature change, color change, and precipitate. Reaction RATE is the FIFTH piece of evidence: same products, but how fast they form depends on conditions. Enzymes in your body (amylase, catalase) are biological catalysts that make life-sustaining reactions fast enough at 37 °C.

I can apply collision theory by...if I need to speed up a reaction, I have FOUR levers: raise temperature, raise concentration, grind reactants into powder (surface area), or add a catalyst. To slow a reaction down (like refrigeration), I do the opposite — lower temperature drops kinetic energy and collisions.

DRAW CONCEPT MODEL Energy diagram: with vs. without catalyst

Sketch the energy diagram (energy y, reaction progress x) for the SAME reaction WITHOUT vs. WITH a catalyst. Show reactant + product levels and the activation-energy (Ea) hill for both — the catalyzed hill is lower. Add a particle-collision inset; label ≥3 word-bank terms.

Word Bank: activation energy · catalyst · collision theory · reactants · products

Energy diagram with energy on y-axis, reaction progress on x-axis. TWO curves: (1) UNCATALYZED — high Ea hill from reactants to a tall peak, then down to products; (2) CATALYZED — same reactant and product levels, but a LOWER peak (lower Ea). Label both Ea hills. Show reactants on left, products on right at the SAME final energy (catalyst doesn't change ΔH). Inset: two particles colliding with arrows labeled 'enough energy + right orientation'. Word bank labels: activation energy, catalyst, collision theory, reactants, products.

≥3 word bank terms labeled

Two Ea hills shown (catalyzed is lower)

Reactant/product levels unchanged by catalyst

CHECK TEST YOUR THINKING Rate each: FALSE ← 1-2-3-4-5 → TRUE · 4 new + 1 last week + 1 spiral

1. Doubling the concentration of one reactant doubles the total amount of product made.

F12345T

2. A catalyst is used up by the reaction it speeds up.

F12345T

3. At a given temperature, every particle in a sample has exactly the same kinetic energy.

F12345T

4. Reaction rate and total amount of product are the same thing — a faster reaction ALWAYS produces more total product.

F12345T

5. [Last week] When something burns, mass disappears because the material is destroyed in the flame.

F12345T

6. [Spiral · C5 Kinetic Energy] A hotter object always contains MORE particles than a colder object of the same material — that is why it has more thermal energy.

F12345T

Pick any TWO statements -- especially any you rated 2, 3, or 4. Justify your rating with evidence:

Statement #___ -- I rated it ___ because:

THINK SCIENTIST CIRCLE DEBRIEF Reflect after your Scientist Circle discussion

AHA! Moment

The one I changed my thinking most about is... catalysts don't push the reaction — they just lower the hurdle so more of the everyday collisions are big enough to count. The reaction was already trying to happen; the catalyst just makes it easier.

Remaining Question

I still wonder... If a catalyst comes out unchanged, why doesn't ONE tiny pinch of catalyst eventually speed up an infinite amount of reaction? What actually wears it out in the real world?

WRITE FOCUS QUESTION REVISIT Final written response

Why does food cook faster on a hot day than a cold day?

Word Bank: reaction rate · catalyst · collision theory · activation energy · concentration · surface area

CLAIM: Food cooks faster on a hot day because higher temperature gives food particles more kinetic energy, so more collisions clear the activation-energy hurdle each second.

EVIDENCE: In the lab, raising temperature from 5 °C to 50 °C sped the same reaction up many times over (~10 °C doubles the rate). Powdered reactants reacted much faster than chunks (more surface area = more collisions). Catalysts sped reactions WITHOUT being consumed by lowering the Ea hill.

REASONING: Collision theory ties it together — reactions need enough-energy collisions in the right orientation. Temperature, concentration, surface area, and catalysts each increase either collision frequency or the fraction of collisions above activation energy. Same products either way; the rate is what changes.